1. Field of the Invention
The present invention generally relates to the general problem of keeping the aspect ratio of images when there is a difference in format between image sources and display panels. More particularly, this invention relates to a circuit and a method for holding a fixed aspect ratio when converting image formats to specific display formats.
2. Description of the Prior Art
FIG. 1a shows a prior art illustration of what happens when a circular source image for a computer display 110 of a given resolution is up-scaled or magnified 150, to a larger format 120. The up-scaled image on the display is distorted. It no longer looks like a circle, but it now looks like an ellipse 120. The original source image was stored in an XGA format of 1024×768 pixels. This resolution of 1024×768 has an aspect ratio of 1024/768=4/3. The display panel format in FIG. 1a is 1280×1024 or SXGA format. This resolution of 1280×1024 has an aspect ratio of 1280/1024=5/4. The result of a different aspect ratio is a distorted circle on the display.
FIG. 1b shows a prior art illustration of what happens when a circular source image 130 of a given resolution is downscaled 160 or de-magnified, to a smaller pixel format. The downscaled image 140 on the display is distorted. It no longer looks like a circle, but it now looks like an ellipse 140. The original source image was stored in a VXGA format of 1600×1200 pixels. This resolution of 1600×1200 has an aspect ratio of 1600/1200=4/3. The display panel format in FIG. 1b is 1280×1024 or SXGA format. This output panel resolution of 1280×1024 has an aspect ratio of 1280/1024=5/4. The result of a different aspect ratio creates a distorted circle on the display.
In the prior art, the general image formats currently used with different aspect ratios are below.                VGA: 640×480=4×3 (aspect ratio=1.33)        SVGA: 800×600=4×3 (aspect ratio=1.33)        XGA: 1024×768=4×3 (aspect ratio=1.33)        SXGA: 1280×1024=5×4 (aspect ratio=1.25)        UXGA: 1600×1200=4×3 (aspect ratio=1.33)When an LCD (or other computer display) controller transfers the input source signal to the display panel the difference in format between the source signal and the target panel is considered. The problem encountered in the prior art is the requirement to keep the aspect ratios the same during the transition from image source to the display panel. In the prior art, when converting VGA, XGA and UXGA signals from the source to a display panel such as an SXGA panel, there are aspect ratio changes to be solved. If the aspect ratio changes are not solved, the images displayed at the panel will be distorted as seen in FIGS. 1a and 1b.         
U.S. Pat. No. 5,748,175 (Shimada, et al.) “LCD Driving Apparatus Allowing for Multiple Aspect Resolution” describes a LCD driver apparatus which allows for multiple aspect resolutions.
U.S. Pat. No. 6,275,306 (Wataya, et al.) “Image Processing System Converting the Pixel Aspect Ratio” discloses an image processing system which converts the pixel aspect ratio.
U.S. Pat. No. 6,191,820 (Kang, et al.) “Device and Method for Converting Aspect Ratio of Video Signal” describes a device and a method for converting the aspect ratio of a video signal.
U.S. Pat. No. 5,983,247 (Yamanaka, et al.) “Data Conversion Apparatus for Reading a Document for a Display Screen and Generating a Display Image for Another Display Screen Which Has a Different Aspect Ratio from the Former Display Screen” discloses a data conversion apparatus for reading a document for a display screen and creating an image for another screen which has a different aspect ratio from the other display screen.